1. Field
The present disclosure relates to apparatus and methods for control of sleep modes in a transceiver and, more particularly, for automated control of different sleep modes using a hardware implemented sleep mode controller.
2. Background
Conservation of energy in battery-powered devices, such as mobile phones, is an important concern in order to maximize the limited energy available to such devices. During operation of mobile devices such as mobile phones, however, it is known that some of the power consuming units within such devices can be temporarily powered down without adversely affecting the performance of the mobile device. This powering down, known as “sleep,” affords power savings since current consuming units only consume power periodically, rather than continuously.
In order to improve the battery life of a device, it is known to place numerous current consuming units within the device into a power saving mode and maintain the system time using low-power sleep circuits. Because of the high current draw (and, thus, power usage) of voltage-controlled temperature-compensated oscillators (VCTCXOs) that are used for accurate system timing in a mobile device, in particular, it is not energy efficient to use such devices to maintain system time for sleep circuits. Accordingly, it is known to maintain system timing during sleep or power saving modes by using a sleep controller consuming much less power and clocked by a crystal oscillator at lower frequency (e.g., 30-60 kHz) rather than the VCTCXO frequency, which is usually much higher (e.g., 19.2 MHz). Usage of the cost effective crystal oscillator as the sleep controller clocking device is at the expense of some accuracy in time keeping because the clock frequency tends to drift with temperature. This clock is otherwise known as the “sleep clock” or “slow clock.” Thus, when the mobile device is asleep, the system clock or “fast clock” (and VCTCXO) is off. The sleep clock is used as a timer to wake up the system. Upon wake up, once the fast clock becomes stable after waking up, system timing is once again handed over to the fast clock.
Furthermore, in certain types of transceivers that receive burst type communications, such as in orthogonal frequency division multiplexed (OFDM) systems, the nature of such systems lend themselves to sleep mode usage due to the periodic nature of when system resources are actually used. In such devices, however, the use of software execution of timing events for shutting down components or waking up components can engender latencies that cause errors or do not result in effective reduction of power consumption during sleep mode due to under utilization of the potentially available time for shutdown of components.